v0.9.0-pre3

• Added mechanism to detect image types by magic numbers
• Removed the SOURCE output pixel format from the list of guaranteed pixels formats to output. Some plugins, like TIFF, cannot output SOURCE pixels
• Display paletted images in the deep-diver C++ demos
• Moved source image properties into a separate struct image -> source_image
• Probing images from memory and custom I/O sources
• Added a log barrier to filter out log messages under a certain level
• The PNG plugin is able to save indexed images
• Added MacOS support